The purpose of this project is to develop an animal model of bioprosthetic cardiac valve failure and to utilize this animal model system to evaluate the pathologic alterations and hemodynamic dysfunction which develop in the valves. We have shown that bioprosthetic valves implanted in juvenile sheep demonstrate the same pathologic alterations of degeneration and calcification as those implanted in humans; however, the development of these alterations is accelerated in sheep as compared to humans. Nearly 300 porcine aortic or bovine pericardial bioprosthetic valves from six different sources have been implanted in the animal model system to assess the characteristics of the pathologic changes, to compare the alterations in different types of valves, to compare the alterations occurring in valves implanted in the mitral versus the tricuspid positions, and to evaluate valves treated prior to implantation with processes to retard or eliminate the calcification process.